Retrieving 65 years of volcano summit deformation from multitemporal structure from motion: The case of Piton de la Fournaise (La Réunion Island)

The structure from motion photogrammetry technique enables use of historical airborne photography to achieve high‐resolution 3‐D terrain models. We apply this method on Piton de la Fournaise volcano (La Réunion), which allows a unique opportunity to retrieve high‐resolution (1.5–0.11 m) digital elevation models and precise deformation maps of the volcano since 1950. Our results provide evidence that the summit volume increased throughout the study period, at a stable rate of 2.2 Mm 3 /yr between 1950 and 2015, with an acceleration up to 8.0 Mm 3 /yr prior to the major 2007 eruption that was accompanied by summit caldera collapse. At the same time, summit deformation was asymmetric, with 9.2 ± 2.5 m of eastward seaward displacement and 1.3 ± 2.5 m to the west during 1950–2015. Our results reveal a temporal evolution in the volcano magma influx rate and deformation. Tracking these fluxes and the long‐lived preferential eastern motion is crucial to mitigate risks associated to flank destabilization.